1. Field of the Invention
This invention relates to a battery can hole detecting apparatus for examining whether or not battery cans formed by drawing are defective due to perforations.
2. Description of the Prior Art
FIG. 6 shows an example of a battery can which has heretofore been in use. The two parts 1 and 2 shown in FIG. 6 are members which constitute the anode section of a battery. One part 1 is a cylindrical member having a flat closed end and an open at the other end. The other part 2 constitutes an anode terminal to be fixedly attached to the closed end surface of the cylindrical member 1. In recent years, however, in order to reduce the number of parts to thereby improve workability and reduce cost and to make effective use of the space in the anode terminal member 2, there has been developed a one-piece battery can as shown in FIG. 7.
The battery can 3 shown in FIG. 7 is obtained by drawing a sheet material on a press. The battery can 3 constitutes the anode section of a battery, but it differs from the example shown in FIG. 6 in that it is formed as a single member. And the closed end has two projections constituting the anode terminal.
The battery can 3 shown in FIG. 7 is suitable for mass production but, on the other hand, it offers problems to be presently described. FIG. 8 shows the process for production of the battery can 3. Usually, the processing steps shown therein are performed on a single press. To obtain the shape of the battery can 3 shown in FIG. 7, the drawing operation is performed roughly in three stages. In the first stage, a sheet material shown at (a) is drawn to a shape shown at (b). The member (b) has a closed flat end. The second stage of drawing provides the shape shown at (c), whereby a single projection results. The final stage of drawing is then performed to provide a shape shown at (d) corresponding to the shape shown in FIG. 7, wherein the can 3 has two projections constituting anode terminal of a battery.
As described above, to obtain the battery can 3 of the shape shown in FIG. 7, a substantial amount of drawing has to be performed. This means rather a radical drawing operation on the blank. As considered from the present level of press technology, it would be difficult to produce battery cans by deep drawing with high accuracy without involving any rejects. In other words, some of the deep drawn battery cans 3, though very few, may have holes resulting from deep drawing. In this connection, it is to be understood that the word "holes" as used herein refers not only to literal holes but also to breaks, cracks, etc. Such holes often form in the corners of the projections at the closed end of the battery can 3. If a battery can, while retaining holes, is assembled as a final product, a electrolytic solution would leak through the holes, thereby making a product unusable. Therefore, it is necessary to withdraw defective battery cans from production to ensure that defective products do not appear on the market.
However, the size of holes resulting from drawing is very small and, moreover, oil has adhered to the products. As a result, holes can hardly be found visually. Further, the number of battery cans formed by drawing is so large that it is practically impossible for the operator to visually inspect battery cans one by one to find holes therein.
For this reason, there is no way but a mechanical one to examine whether or not battery cans have holes. In order to improve the workability and increase the operating efficiency in the production process, it is preferable to examine battery cans as they are drawn on a press machine and delivered therefrom. To provide an operative association of the press and the hole detecting mechanism, it could be contemplated to operate the hole detecting mechanism with the same cycle time as that of the press. However, in a press, the cycle time required for drawing one battery can is very short. For example, it is 1 second per unit. In this case, battery cans will be fed to the hole detecting mechanism at a rate of one unit per second, but it is difficult to make a check in one second of whether or not a battery can has a hole.
For this reason, usually, the hole detecting mechanism would be separated from the press for performing the can hole detection separately from the drawing of the cans. However, it is desirable to perform a continuous detection of holes in battery cans as they successively come out of a press for increasing efficiency.